Vaccination is increasingly used to control the infectious diseases in animals. Adjuvants are frequently used in vaccines because they are able to increase the humoral and/or cellular immune response to an antigen. Vaccines are often formulated as emulsions because the emulsion can act as an adjuvant, and has the property of retaining the antigen as a depot at the site of injection. Emulsifiers are commonly used in emulsion vaccines. Besides using emulsifiers, the stability of the emulsion vaccines may also be achieved through reducing the droplet size of the emulsion by mechanical means.
U.S. Pat. No. 5,084,269 relates to an adjuvant formulation containing lecithin in combination with mineral oil, which produces less irritation within the host animal, and simultaneously induces increased systemic immunity. Compositions according to U.S. Pat. No. 5,084,269 are in commercial use under the trade name AMPHIGEN®, a trademark of Pfizer, Inc.
Generally, bacterial antigens are unstable when heated and even brief exposure to elevated temperatures can reduce the activity of the antigens. For example current anthrax vaccines can lose all biological activity with 48 hours at 37° C. (S. Sing, N. Ahuja, V. Chauhan, E. Rajasekaran, W. S. Mohsin, R. Bhat, and R. Bhatnagar; Bioche. Biophys. Res. Commun. 2002 Sep. 6; 295(5):1058-62).